Posted A week ago
Completely zeroing out an Android phone's entire internal storage isn't possible unless you have specialized hardware, which only the manufacturers seem to possess. Certain partitions are write protected, rooted or not. You can't even do it via fastboot. I'm sure it would work on an SD though. But is there another way to reset the SD's flash storage, without writing zeros, which will take many hours? I know it can be done with an SSD, Parted Magic has an option for ATA/NVMe hardware low level secure erase, which I've never felt a need to use yet.
The manufacturer in question, while not being particularly friendly to the modding community, has still been known to honor warranties on modded devices, though doing so generally violates warranty, so they have no obligation. Nevertheless, I RMAed a modded phone to them before, they fixed it without complaint. But I didn't mention rooting etc on the phone either. Naturally since the device still boots I would flash stock firmware first, reversing all self-made changes. I personally could care less if they see my files, it's not like I'm storing blueprints for a biochemical weapon or something. I doubt they will care about my peculiar porn fetishes or whatever. If one of the techs wants to fap to my pic collection then be my guest, but fix it and return it regardless.